Data processing

ABSTRACT

A method of routing messages includes receiving a request message from an originating device to be forwarded to one of a plurality of target devices, the request message having a first network address as a source address identifying the originating device. The first network address of the request message is dynamically mapped to a second network address of a selected target device, and the first and second network addresses are stored in association with each other as address mapping information. The method also includes forwarding the selected target device using the second network address. The routing device receives from the target device an error message in relation to the request message, and identifies the originating device which originated the request message using the address mapping information and the second network address of the target device which issued the error message.

BACKGROUND

The present invention relates to a data processing apparatus and methodfor routing messages.

It is common for client devices to communicate request messages toserver devices, with the server then delivering or carrying out arequested service. One example of this is a web server in which a webapplication at a client device transmits a HTTP (Hypertext TransferProtocol) request to a physically remote web server, with the web serverbeing responsive to the HTTP request to deliver a web page to the clientdevice. Another example is a messaging server in which a messagingapplication at a client device transmits a request to a physicallyremote messaging server to deliver a message to another device. Ineither case, it is also common for a cluster of server devices to beused to improve capability and resilience. In this case, a workloadbalancing router may be used to spray request messages evenly across theseparate server devices within the cluster. The request messages may beprocessed at the server devices in a message queue (MQ), by a queuemanager, providing a transport to back end systems. A NAT (NetworkAddress Translation) router may be used as the workload balancingrouter.

Where a NAT router is used, a source IP address of the request messagereceived from a client device for forwarding on to one of the serverdevices is mapped to a destination IP address by the NAT router fortransmission to the server device indicated by the destination address.Generally, the allocation of the destination IP address is carried outdynamically. In some cases, the client device and/or server device maymisbehave, or a request message may make a request of the server devicewhich cannot be fulfilled. This may cause an error condition at theserver device (because it cannot or will not service the request), whichneeds to be resolved before further request messages (from the sameclient device/application) can be serviced. As a result, furthermessages from the same client device/application may flood the errorlogs at the queue manager of that web server.

SUMMARY

According to an aspect of the present invention, there is provided amethod of routing messages, comprising: receiving, at a routing device,a request message from an originating device to be forwarded to one of aplurality of target devices, the request message having a first networkaddress as a source address identifying the originating device;dynamically mapping the first network address of the request message toa second network address of a selected target device, storing the firstand second network addresses in association with each other as addressmapping information, and forwarding the request message to the selectedtarget device using the second network address; receiving from thetarget device an error message in relation to the request message;identifying the originating device which originated the request messageusing the address mapping information and the second network address ofthe target device which issued the error message; and configuring therouting of a later request message from the identified originatingdevice.

Other aspects of the present invention include an apparatus for routingmessages and a computer program for same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a client device and a server exchangingmessages via a NAT router;

FIG. 2 schematically illustrates a series of message exchanges androuter operations for handling error conditions;

FIG. 3 is a schematic flow diagram of a method of configuring the NATrouter in response to an error condition at a server device; and

FIG. 4 is a schematic flow diagram of a method of handling requestmessages received from client devices.

DETAILED DESCRIPTION

Referring to FIG. 1, a client (originating) device 1 running a webapplication is communicating with a server (target) device 3 a torequest the web server 3 a to establish a HTTP connection or to transmita particular web page or file back to the client device 1. The webserver 3 a is one of a plurality of web servers in a cluster of webservers. Two other web servers 3 b, 3 c are also shown. Thecommunication of messages from the client device 1 to the web serverdevice 3 a is via a NAT router 2. The NAT router 2 may be an F5 loadbalancer. The NAT router here provides two main (conventional)functions. Firstly, it serves to provide workload balancing between theweb servers 3 a, 3 b, 3 c, by routing messages to a selected one of theservers. Secondly, it provides for network address translation (NAT) ofinbound (from the client device 1 towards the servers 3 a, 3 b, 3 c) andoutbound (from the servers 3 a, 3 b, 3 c towards the client device 1)messages. The NAT router 2 provides for an IP address range of 9.20.x.xas seen by the server cluster, with inbound messages having their sourceaddress translated to an inside network address within this range. Whileonly a single client device is shown in FIG. 1 in the interests ofsimplicity, it will be appreciated that there will generally be manyclient devices requesting services of the server cluster via the router2.

The NAT router comprises a controller 22 which provides overall controlof routing, address translation and error handling, and whichappropriately directs messages between the client device 1 and the webservers 3 a, 3 b, 3 c. Network address translation (inbound) is carriedout by an address translator 24, which dynamically allocates a newnetwork (IP) address for the client device 1 when a request message isreceived from the client device 1. In particular, the request messagewill have a source IP address (outside address) identifying theoriginating client device 1 to the router 2. However, this outsideaddress is not suitable for use within a server domain defined betweenthe router 2 and the servers 3 a, 3 b, 3 c, hence the requirement fornetwork address translation. Specifically, the router 2 maps the outsideaddress (referred to herein as a first network address) into an insideaddress suitable for use in the server domain, and which corresponds tothe NAT router itself. It also maps the first network address to asecond network address corresponding to a target device (server) towhich the request message is to be forwarded, thereby implementingrouting. A correspondence between the first network address and thesecond network address is stored in a dynamic NAT table 242 until theserver has responded to the request message. Generally, each time a newrequest message is received from a given client device a new secondnetwork address is allocated (and thus potentially a different server),however in some cases (for example if only a short period of time haspassed since the previous request message from that client device) thesame second network address may be used again if it is already presentin the NAT table 242 and is not allocated to a different client device.It will also be understood that the dynamic routing may coincidentallymap a particular client device to the same server on multiple occasions.While not directly relevant to understanding the present technique, itwill be appreciated that outbound network address translation may becarried out in the same way so that inside addresses used within theserver domain to represent the servers 3 a, 3 b, 3 c are translated intooutside addresses suitable for use outside of that domain. It will befurther appreciated that the client device 1 generally does not need tobe able to distinguish between the servers 3 a, 3 b, 3 c—since routingof messages to an appropriate one of these is conducted by the router 2.In other words, the server cluster as a whole (with the router 2 actingas a gateway) can be treated externally as a single IP address.

Upon receipt of a request message from the client device 1, thecontroller 22 selects which of the web servers 3 a, 3 b, 3 c shouldservice the request (and therefore two which the request message shouldbe forwarded) based on a configuration file 26 and a routing algorithm28. The routing algorithm 28 may be used to select an appropriate one ofthe servers 3 a, 3 b, 3 c to service the request in order to balance theworkload within the cluster. The IP address of the selected server isused as the second network address.

It can be seen from FIG. 1 that a request message REQ has beentransmitted from the client device 1 to the router 2. The controller 22has selected the web server 3 a to service the request (based on therouting algorithm 28 and/or the configuration file 26), translated thefirst network address into a second network address corresponding to theselected web server 3 a, and has forwarded the request as a requestmessage REQ′ to the web server 3 a at the second network address. If theweb server 3 a were to be able to service the request, then the requestwould be serviced, which might for example result in one or moreresponse messages and message content being conveyed (through the router2) back to the client device 1. However, in the present case the webserver 3 a is unable to service the request, and therefore an errorcondition handler 30 running on the web server 3 a transmits an errormessage ERR back to the router 2, and in particular to the controller22. The error message ERR may contain the second network address (serverIP address) and a time stamp of the time of generation of the errormessage ERR. However, provided that the router 2 is able to determinethe origin of the error message ERR, at a minimum it is only necessaryfor the error message ERR to indicate that an error condition has arisenon a particular server device. The controller 22 is responsive to theerror message ERR to look up the second network address of the server inthe error message ERR in the dynamic NAT table 242. In this way, thecontroller 22 can identify the first network address associated with thesecond network address, which identifies the client device whichtriggered the error condition. A NAT router only preserves dynamicaddress mapping information for the time required for the server tohandle the request message and provide a response message, and for therouter to forward the response message on to the client device. As aresult, the error message ERR should be sent to the NAT router prior toa response message being sent from the server to the NAT router,otherwise the dynamic NAT table 242 may no longer hold the informationrequired to identify the originating (client) device.

The identity of the client device can optionally be provided to serverdevice 3 a, or an administrator thereof to assist with resolving theerror, or for error logging purposes. The controller 22 may thenassociate the first network address of the client device 1 with a third,static, network address in a static NAT table 244, the third networkaddress being the IP address of one of the server devices. In this case,subsequent messages from the first network address will always (untilthe association between the first network address and the third networkaddress is revoked) be forwarded to the server device 3 a indicated bythe third network address. It will be appreciated that a single tablecould be used instead of separate tables for the dynamic and staticaddress mappings, with flags or characteristics of the address structurebeing used to distinguish dynamic and static addresses from each other.As an alternative to using static network addresses, the controller maymark the first network address for pass-through mode, in which the first(outside) network address is retained as a source address whenforwarding messages from the client device 1 to the server 3 a, ratherthan carrying out network address translation.

It will be appreciated from the above that when a target server 3 aapplication detects an error as a response to a client request, it sendsto the router 2 an event which preferably includes the network addressof the server. At any given time, the server is only servicing a requestfrom one client device, and so by identifying the server and checkingthe NAT table it is possible to identify the client device which madethe request which triggered an error condition. The NAT router 2therefore receives the error event, and looks up the originating IPaddress, dynamically switching that address into a static mapping orstraight pass-through. As a result of this, when the server firesanother error event, this time it contains an “outside” (first) IPaddress in the case of a pass-through, or a static (third) IP address.When the NAT router 2 looks up and discovers that the IP addressincluded in the event is static or outside, it knows that the targetserver has the means to identify the originating IP (via the look uptable 244 if static) and the router 2 also knows that this client devicehas already generated an earlier error (because the address is not adynamic NAT address) and if configured to do so, can now block orredirect any further requests from that client until it has beeninformed that the error has been resolved (by another protocol, or amanual step).

Referring to FIG. 2, an ordered sequence of operations A to H at therouter 2 is shown. The three network entities shown in the operationsare the client device 1, the router 2 and the server 3 a. For eachoperation, an entity shown in dashed lines is not involved in thatoperation. Operation A is the receipt (from the client device 1) at therouter 2 of a first request message REQ1, having a first network addressas a source address, the address translation of the first networkaddress into a second network address, which is then used as thedestination address for a forwarded version of the first request messageREQ1, denoted REQ1′, which is transmitted from the router 2 to theserver 3 a. As mentioned above, an association between the first networkaddress and the translated second network address is stored in thedynamic NAT table 242.

Operation B is the generation of an error message at the server 3 a inresponse to an error condition arising in relation to the request madeby the request message REQ1′, and the transmission of the error messageERR1 to the router 2, along with the second network address, whichidentifies to the router 2 the server 3 a. The router 2 refers to theaddress mapping information to identify the first network address of theclient device 1 which issued the request message REQ1 which caused theerror condition at the server 3 a. The first network address mayoptionally be communicated to the server 3 a for error logging purposes,or in some cases to aid diagnosis of the error (and resolution of theerror if this requires remedial action at the client device 1). Thefirst network address may also optionally be used to address a statusupdate message to the client device 1 to advise it that there is aproblem in servicing the request it made. At operation B, the router 2also updates the address mapping information (which may be implementedas the NAT tables 242, 244 described above) to associate the firstnetwork address with either a third, static, network address, or tooperate in a pass-through mode in which the first network address isretained and subsequent request messages received from the client device1 are forwarded to the server 3 using the (outside) first networkaddress as the source address.

Operation C is the receipt (from the client device 1) at the router 2 ofa second request message REQ2, having a first network address as asource address, the address translation of the first network addressinto a third, static, network address (for example using the static NATtable 244), which is then used as the destination address for aforwarded version of the second request message REQ2, denoted REQ2′,which is transmitted from the router 2 to the server 3 a. Operation D isthe generation of a further error message ERR2 at the server 3 a inresponse to the receipt of a further request from the client device 1while the previously triggered error condition has not yet beenresolved, and the transmission of the error message ERR2 to the router2, along with the third network address associated with the firstrequest message REQ2′.

In operation D, the router 2 identifies that a second error message hasbeen generated in relation to requests made by a particular clientdevice, based on the fact that static network address translation or apass-through mode is being used in relation to messages from that clientdevice, that is, the third network address appears in the static NATtable 244. This may be determined by referring to the address mappinginformation (dynamic NAT table 242 and static NAT table 244). As aresult of this determination, the router 2 may configure routinginformation in the configuration file 26 to cause any further requestmessages from the client device 1 to be handled differently. The router2 may also be responsive to this determination to alter the thirdnetwork address specified in the static NAT table 244 to indicate adifferent server device. The first network address (obtained from one ofthe NAT tables 242, 244) may also optionally be used to address a statusupdate message to the client device 1 to advise it that there is orcontinues to be a problem in servicing the request it made. It will beappreciated that while operations C and D are described with referenceto static network address translation, the same principles would applyfor the use of pass-through of the first network address.

Operation E is the receipt (from the client device 1) at the router 2 ofa third request message REQ3, having a first network address as a sourceaddress, and a decision at the router 2 not to forward the third requestmessage REQ3 to the server 3 a, based on the presence of the firstnetwork address in the static NAT table 244, and information in theconfiguration file 26. The operation E will be conducted each time afurther request message is received from the client device until theerror condition at the server device 3 a has been resolved. Operation Fis the generation of an error resolution message RES1 at the serverdevice 3 a and its transmission to the router 2 in association with thethird network address (or first network address in the case ofpass-through mode). The router 2 is responsive to receipt of the errorresolution message RES1 to update the routing table in relation to thefirst network address/client device 1 to reinstate the original routingscheme (which might be to direct future requests from the client device1 to the server device 3 a, or might be to utilise the original workloadbalancing algorithm). More specifically, the router 2 is responsive toreceipt of the error resolution message RES1 to update the addressmapping information (for example by deleting the relevant entry in thestatic NAT table 244) to revert to dynamic network address translation(using the dynamic NAT table 242) for the first network address of theclient device 1. In this way, the system state is reset to its conditionprior to the error condition having been triggered at the server 3 a.Operation G is the receipt (from the client device 1) at the router 2 ofa fourth request message REQ4, having a first network address as asource address, the address translation of the first network addressinto a second network address, which is then used as the destinationaddress of a forwarded version of the first request message REQ4,denoted REQ4′, which is transmitted from the router 2 to the server 3 a.An association between the first network address and the translatedsecond network address is stored in the dynamic NAT table 242. In otherwords, operation G is substantially the same as operation A followingthe resolution of the error condition at the server 3 a, and thenotification of this resolution to the router 2.

Referring to FIG. 3, an example method of updating address mappinginformation and routing information at the router 2 in response to anerror condition is shown. At a step A1 an error message is received atthe router 2 from a server. Network address information identifying theserver is extracted from the error message. At a step A2, the NAT tablesare consulted to determine whether the extracted network address is adynamic NAT address (second network address) or a static NAT address(third network address). If it is determined that the extracted networkaddress is a dynamic NAT address, then the router 2 knows that this isthe first error message (that is, message ERR1 in FIG. 2) from theserver indicating the occurrence of a new error condition. In this case,at a step A3 the NAT tables are updated to switch from the use of adynamic NAT address to either a static NAT address or a pass-throughmode in which the original source (outside) address (first networkaddress) of the client device 1 is used directly as a source addresswhen communicating further request messages to the server. At a step A4the server is notified of the identity of the originating client devicefor data logging/resolution purposes. If at the step A2 it is determinedthat the extracted network address is a static NAT address, or anuntranslated pass-through network address, then at a step A5 theconfiguration file 26 is updated to indicate that subsequent messagesfrom this client device should be inhibited from being forwarded to theserver. In other words, the step A5 is carried out where the errormessage is determined to be message ERR2 in FIG. 2.

Referring to FIG. 4, an example method of handling routing to a serverdevice is shown. FIG. 4 should be read in association with FIG. 3, whichexplains how the NAT tables 242, 244 and configuration file 26 aremodified in response to error messages from servers. At a step B1, arequest message is received at the router 2 from a client device. At astep B2, it is determined whether there is an ongoing error condition inrelation to a request previously made by the originator of the requestmessage, by checking the static NAT table 244. If the IP address of theoriginator of the request message is not listed in the NAT table 244,then an error condition is assumed not to exist. In this case, at a stepB3 the balancing algorithm is applied to select a suitable server toservice the request, an IP address for the selected server is allocated,and the dynamic NAT table 242 updated to store the mapping between theIP address of the originator device and the IP address of the selectedserver, and then the request message is forwarded to the selected serverusing its IP address at a step B4. If however at the step B2 it isdetermined that the IP address of the originator of the request messageis listed in the static NAT table 244, then an error condition isassumed.

If an error condition has been identified at the step B2, then at a stepB5 a type of the request message is identified. The type may for examplebe the type of service being requested (in the context of a web serverthe type may be accessing a particular type of web page, or downloadinga file versus accessing a web page for example). If the request messageis of a first type, then it may be determined that it can be servicednormally even though an error condition is ongoing. This may be becausethe type of the request message, or the type of service being requested,is different from the type of service which triggered the errorcondition. In the case that the request is determined to be of a firsttype, the steps B3 and B4 are carried out, as described above. If therequest is determined to be of a second type, then the priority of therequest message is determined at a step B6. The priority of the requestmessage may be an inherent property of the message (for example based onheader fields within the request message), or may be based on anapplication defined priority for messages from a particular clientdevice, such priority information being received from the server withinthe error message. For example, an error message may both indicate thepresence of an error, and also indicate that the nature of the requestshould be considered unimportant (for example not time critical).Alternatively, the error message may indicate instead that the nature ofthe request is important (for example it is time critical). If thepriority of the request message is considered to be low, then therequest message is simply blocked at the router 2 at a step B7, and goesno further. If however the priority of the request message is consideredto be high, then the request message is redirected to another server ata step B8. The server to which the request message is redirected may bechosen from the remaining servers (that is, the servers other than theserver at which an error condition is ongoing) based on the routingalgorithm described above. Rules for handling request messages followingan error condition may be specified in the configuration file. Theserver originating an error message may instruct the router how furthermessages should be handled by way of updating the configuration file.The rules contained within the configuration file may include thoserelating to type and priority.

It will be appreciated that if a client device does not have its requestsatisfied, it may retransmit a request message. By way of the abovetechnique, while the first and second request messages may reach theserver, subsequent messages may be redirected to another server, whichis able to service the request, which is preferable (from a clientdevice perspective) to an arrangement in which the request continues tobe unsuccessfully serviced by a server which is experiencing an errorcondition. Further, from the server perspective, a server may issue anerror message to the router to reject a request and effectively forcethe router to use another server instead, reducing the number ofnon-serviceable request messages received by the server. It will beunderstood that variations on the above implementation can be provided.For example, the blocking or redirecting of subsequent request messagesmay be triggered by a first, second, third or later error message bysimply tracking at the NAT router the number of error messages receivedin relation to the same client device or network address (for example inthe configuration file 26). In one example, the receipt of one or moreerror messages at the router in relation to a particular client devicemay cause the router to add that client device to a block list of clientdevices in relation to which incoming request messages should beblocked. More generally, the error message effective requires the router2 to disable dynamic routing for a specific network address—in the aboveexample either by dynamically switching to a static NAT address or to astraight pass-through mode—bypassing the network address translationalgorithm altogether. The server 3 a may include in an error message aninstruction as to whether to redirect to another server or blockentirely further request messages. This instruction may be based on thereason that the error condition has arisen.

In one example implementation of a web server, the priority of a requestmessage may relate to whether it is requesting a premium service. If thecurrently selected server is not capable of providing the premiumservice then an error message may be transmitted to the router. If noneof the servers are capable of providing the premium service, thensubsequent request messages may simply be blocked entirely (preferablywith the client device being notified accordingly), while if some of theservers in the cluster are capable of providing the premium service thenthe router 2 will keep selecting servers in accordance with itsalgorithms until the request is accepted by one of the servers.

In another example implementation, the priority of a request message mayrelate to whether the requesting client device is local to (eithergeographically or in network topography terms) the server cluster ordistant to the server cluster. A high priority request may be one from alocal client device while a low priority request may be one from adistant client device. The location information required for the routerto determine this may for example be available in header informationwithin the request message.

In another example, a further level of priority may be a criticalrequest message, which is forwarded to the server having the errorcondition in spite of the error condition.

Error conditions may be triggered due to a lack of memory or disk spaceresources at a server. In this case, a request which cannot be serviceddue to a lack of disk space or memory at a given server will be rejectedwith an error message as described above, which will result in therouter allocating subsequent requests from that client device to adifferent server device within the cluster.

While all inbound connections/request messages/client devices could bemapped to unique inside IP addresses on the internal (server/routerdomain) network, in some cases two or more client devices could bemapped to the same internal IP address, but with different port numbersbeing used to distinguish between these. In this case, the networkaddresses referred to above may be taken to include the IP address andport number taken in combination.

It will therefore be appreciated that the above described techniquemakes it possible for a server (for example an MQ server) in a loadbalanced environment to be able to determine the original or source IPaddress of a remote client after the source IP address has been subjectto network address translation by a NAT router. This makes it possiblefor backend administrators of a server cluster to identify a misbehavingclient device or application even though the server itself is unable toreverse the network address translation to uniquely identify the clientdevice.

While the example of a multitude of web application servers acting asclients is used above, it will be appreciated that the present techniqueof routing request messages may be applied to any kind of clientapplication. For example, the server devices may be messaging serversand the request messages may be requests to deliver message informationto another device. Generally, the present technique allows anapplication server to feed back to a NAT router error conditionsassociated with the application server or a request received at theapplication server (through the NAT router), permitting subsequentrouting to be controlled. It can be viewed that this technique breaksthe conventional OSI layer model, by permitting an application layercomponent (server application) to enlist a transport layer component(routing decisions and address translation at the NAT router) in anerror handling routine.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium include the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structure in a groove having instructions recordedthereon, and any suitable combination of the foregoing. A computerreadable storage medium, as used herein, is not to be construed as beingtransitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may computercopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FGPA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture instructing instructions which implement aspectsof the function/act specified in the flowchart and/or block diagramblock or blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality and operation of possible implementations ofsystems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart of block diagrams may represent a module, segment, or portionof instruction, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

What is claimed is:
 1. A method of routing messages, comprising:receiving, at a routing device, a request message from an originatingdevice to be forwarded to one of a plurality of target devices, therequest message having a first network address as a source addressidentifying the originating device; dynamically mapping the firstnetwork address of the request message to a second network address of aselected target device, storing the first and second network addressesin association with each other as address mapping information, andforwarding the request message to the selected target device using thesecond network address; receiving from the target device an errormessage in relation to the request message; identifying the originatingdevice which originated the request message using the address mappinginformation and the second network address of the target device whichissued the error message; and configuring the routing of a later requestmessage from the identified originating device.
 2. A method according toclaim 1, wherein configuring the routing comprises configuring therouting device to not forward a later message received from theidentified originating device to any of the target devices.
 3. A methodaccording to claim 1, wherein configuring the routing comprisesconfiguring the routing device to forward a later message received fromthe identified originating device to one of the plurality of targetdevices other than the target device from which the error message hasbeen received.
 4. A method according to claim 1, wherein configuring therouting comprises identifying a priority or type of a subsequent messagereceived from the identified originating device, and determining whetheror not to forward that message to the target device from which the errormessage has been received in dependence on the priority or type of thesubsequent message.
 5. A method according to claim 1, whereinconfiguring the routing comprises identifying a priority or type of asubsequent message received from the identified originating device, andeither blocking the subsequent message entirely or redirecting it to adifferent one of the target devices in dependence on the identifiedpriority or type of the subsequent message.
 6. A method according toclaim 1, comprising updating the address mapping information toassociate the first network address with a third, static, networkaddress of a target device to which subsequent messages from theoriginating device should be sent, in response to receipt of the errormessage.
 7. A method according to claim 1, comprising updating theaddress mapping information to indicate that the first network addressshould be used when transmitting to a selected target device subsequentmessages received from the originating device.
 8. A method according toclaim 6, comprising: receiving at the routing device a second requestmessage following the request message which triggered the error messagefrom the originating device, and forwarding the second request messageto a server at the third network address, receiving from the selectedtarget device a second error message in relation to the second requestmessage; and updating routing information at the routing device toconfigure the routing device to inhibit routing of later requestmessages from the identified originating device to the target device. 9.A method according to claim 7, comprising: receiving at the routingdevice a second request message following the request message whichtriggered the error message from the originating device, and forwardingthe second request message to a server using the first network address,receiving from the selected target device a second error message inrelation to the second request message; and updating routing informationat the routing device to configure the routing device to inhibit routingof later request messages from the identified originating device to thetarget device.
 10. A method according to claim 1, comprising selectingat the routing device a target device to which the request message is tobe sent based on a workload balancing algorithm.
 11. A method accordingto claim 1, wherein the target device generates the error message inresponse to detection of an error condition.
 12. A method according toclaim 1, wherein the error message indicates that the target devicecannot service the request made by the request message.
 13. A methodaccording to claim 1, wherein the target device is responsive to a lackof available memory at the target device to issue the error message. 14.A method according to claim 1, comprising receiving an error resolutionmessage from the target device from which the error message wasreceived, and in response to the error resolution message reconfiguringthe routing device to dynamically map request messages from theidentified originating device.
 15. A method according to claim 1,wherein the target devices are web servers and the request message is anhttp request message.
 16. A method according to claim 1, wherein thetarget devices are messaging servers and the request message is arequest to deliver message information to another device.
 17. A systemfor routing messages, comprising: an originating device; a plurality oftarget devices; and a routing device, operable: to receive a requestmessage from the originating device to be forwarded to one of the targetdevices, the request message having a first network address as a sourceaddress identifying the originating device; to dynamically map the firstnetwork address of the request message to a second network address of aselected target device; to store the first and second network addressesin association with each other as address mapping information; toforward the request message to the selected target device using thesecond network address; to receive from the selected target device anerror message in relation to the request message; to identify theoriginating device which originating the request message using theaddress mapping information; and to configure the routing of a laterrequest message from the identified originating device.
 18. A computerprogram product for routing messages, the computer program productcomprising a computer readable storage medium having programinstructions embodied therewith, the program instructions executable bya data processing apparatus to cause the data processing apparatus toperform a method comprising: receiving, at a routing device, a requestmessage from an originating device to be forwarded to one of a pluralityof target devices, the request message having a first network address asa source address identifying the originating device; dynamically mappingthe first network address of the request message to a second networkaddress of a selected target device, storing the first and secondnetwork addresses in association with each other as address mappinginformation, and forwarding the request message to the selected targetdevice using the second network address; receiving from the targetdevice an error message in relation to the request message; identifyingthe originating device which originated the request message using theaddress mapping information and the second network address of the targetdevice which issued the error message; and configuring the routing of alater request message from the identified originating device.